Seepage Characteristics And Productivity Evaluation Of Horizontal Well In Marine Thick Reservoir

The sea-level low-permeability gas reservoirs are different from the characteristics of conventional gas reservoirs.The special geographical environment at sea determines their exploitation cycle is relatively short,and the development of high-speed economy needs to be carried out to recover the cost as soon as possibleThe reservoirs of thick and low permeability gas reservoirs are usually characterized by low porosity,low permeability,and strong heterogeneity,and horizontal well development is required to meet the requirements of economic development.The seepage mechanism of thick and low permeability gas reservoirs is complex.Combined with the experimental results,the slippage effect,starting pressure gradient,stress sensitivity,high-speed non-Darcy and water lock damage in low-permeability gas reservoirs are analyzed.Based on the seepage mechanism of thick-bed low-permeability gas reservoirs,this paper compares the classical steady-state horizontal well productivity research methods,the establishment of multi-layer unsteady horizontal well productivity models and numerical simulation methods to the horizontal well productivity of thick and low-permeability gas reservoirs.research.The main research results obtained in this paper are as follows:(1)Analysis of the pore structure of thick-bed low-permeability gas reservoirs shows that primary pores are less conserved,secondary pores account for 60%to 75%of the total pore volume,and although micropores are relatively developed,their pore sizes are smaller and their connectivity is worse.Little,the role of micro-fissure is to improve the seepage ability of the reservoir.(2)Analysis of percolation mechanism shows that:① The slip-off effect occurs under lower pressure conditions,and the waste pressure of the gas reservoir is far greater than the low pressure of the slip-off effect;② The actual gas seepage velocity is faster and there is no low velocity in the formation.The condition of seepage can not be considered the starting pressure gradient;③The seepage of fluid in gas reservoir is high-speed seepage,and its seepage law does not conform to the characteristics of Darcy’s seepage law;④ the reservoir stress is sensitive due to the decrease of formation pressure,and the reservoir permeability is damaged;⑤ There are two main factors that cause the water lock effect:capillary effect and Jiamin effect.(3)Comparing and analyzing the classic steady-state horizontal well productivity formula,and comparing the actual parameters of horizontal wells in gas reservoirs,the optimal thickness,permeability ratio Kh/Kv and horizontal well length under eccentricity are studied.The horizontal permeability ratio is better.The smaller the vertical permeability,the longer the optimal length of the horizontal well and the better the horizontal well production.(4)Establish a seepage equation that takes into account the reservoir stress sensitivity,high-speed non-Darcy,and inter-layer permeability.The differential equations of seepage are solved by using Laplace transform and Green’s function.The effects of reservoir thickness permeability ratio,horizontal section length and high-speed non-Darcy coefficient on horizontal well productivity under non-steady state conditions are analyzed.(5)Using the established single-well model for thick and low permeability gas reservoirs,compare horizontal well parameters such as:horizontal section length,fracture length,number of fractures,horizontal well location,and horizontal well spacing in thick and low permeability gas reservoirs.